Most effective airborne toxins don't care if you hold your breath - they're contact toxins, not inhaled ones.
The pixie will only declare that I missed a spot once. In every following use of the spell ever I'll remember to declare that I didn't miss a spot first.
Vacuum is a fairly effective attack. If it's physical, you get explosive decompression of targets that breathe and boiling internal fluids on targets that don't. If it is a power vacuum, you get people's lives or souls torn out. If it is an energy vacuum, you get areas and people flash-frozen.
Basically, an attack is something you introduce into the story. You get to describe the effect you want - not the defender. And if your storytelling is up to snuff, you can paint enemies into corners for their defense. Even if you don't, they'll have to expend resources (such as declarations, aspects and fate points) to avoid being cornered in that way.